The present invention relates to resilient (spring) contact (interconnection) elements (structures) suitable for effecting pressure and/or compliant connections between electronic components and, more particularly, to microminiature spring contact elements.
Commonly-owned U.S. patent application Ser. No. 08/152,812 filed Nov. 16, 1993 (now U.S. Pat. No. 4,576,211, issued Dec. 19, 1995), and its counterpart commonly-owned copending xe2x80x9cdivisionalxe2x80x9d U.S. patent application Ser. Nos. 08/457,479 filed Jun. 1, 1995 (status: pending) and Ser. No. 08/570,230 filed Dec. 11, 1995 (status: pending), all by KHANDROS, disclose methods for making resilient interconnection elements for microelectronics applications involving mounting an end of a flexible elongate core element (e.g., wire xe2x80x9cstemxe2x80x9d or xe2x80x9cskeletonxe2x80x9d) to a terminal on an electronic component, coating the flexible core element and adjacent surface of the terminal with a xe2x80x9cshellxe2x80x9d of one or more materials having a predetermined combination of thickness, yield strength and elastic modulus to ensure predetermined force-to-deflection characteristics of the resulting spring contacts. Exemplary materials for the core element include gold. Exemplary materials for the coating include nickel and its alloys. The resulting spring contact element is suitably used to effect pressure, or demountable, connections between two or more electronic components, including semiconductor devices.
Commonly-owned, copending U.S. patent application Ser. No. 08/340,144 filed Nov. 15, 1994 and its corresponding PCT patent application No. PCT/US94/13373 filed Nov. 16, 1994 (WO95/14314, published May 26, 1995), both by KHANDROS and MATHIEU, disclose a number of applications for the aforementioned spring contact element, and also discloses techniques for fabricating contact pads at the ends of the spring contact elements. For example, in FIG. 14 thereof, a plurality of negative projections or holes, which may be in the form of inverted pyramids ending in apexes, are formed in the surface of a sacrificial layer (substrate) These holes are then filled with a contact structure comprising layers of material such as gold or rhodium and nickel. A flexible elongate element is mounted to the resulting contact structure and can be overcoated in the manner described hereinabove. In a final step, the sacrificial substrate is removed. The resulting spring contact has a contact pad having controlled geometry (e.g., sharp points) at its free end.
Commonly-owned, copending U.S. patent application Ser. No. 08/452,255 filed May 26, 1995 and its corresponding PCT patent application No. PCT/US95/14909 filed Nov. 13, 1995 (WO96/17278, published Jun. 6, 1996), both by ELDRIDGE, GRUBE, KHANDROS and MATHIEU, disclose additional techniques and metallurgies for fabricating contact tip structures on sacrificial substrates, as well as techniques for transferring a plurality of spring contact elements mounted thereto, en masse, to terminals of an electronic component (see, e.g., FIGS. 11A-11F and 12A-12C therein).
Commonly-owned, copending U.S. Provisional Patent Application No. 60/005,189 filed May 17, 1996 and its corresponding PCT patent application No. PCT/US96/08107 filed May 24, 1996 (WO96/37332, published Nov. 28, 1996), both by ELDRIDGE, KHANDROS, and MATHIEU, discloses techniques whereby a plurality of contact tip structures (see, e.g, #620 in FIG. 6B therein) are joined to a corresponding plurality of elongate contact elements (see, e.g., #632 of FIG. 6D therein) which are already mounted to an electronic component (#630). This patent application also discloses, for example in FIGS. 7A-7E therein, techniques for fabricating xe2x80x9celongatexe2x80x9d contact tip structures in the form of cantilevers. The cantilever tip structures can be tapered, between one end thereof and an opposite end thereof. The cantilever tip structures of this patent application are suitable for mounting to already-existing (i.e., previously fabricated) raised interconnection elements (see, e.g., #730 in FIG. 7F) extending (e.g., free-standing) from corresponding terminals of an electronic component (see. e.g., #734 in FIG. 7F).
Commonly-owned, copending U.S. Provisional Patent Application No. 60/024,555 filed Aug. 26, 1996, by ELDRIDGE, KHANDROS and MATHIEU, discloses, for example at FIGS. 2A-2C thereof, a technique whereby a plurality of elongate tip structures having different lengths than one another can be arranged so that their outer ends are disposed at a greater pitch than their inner ends. Their inner, xe2x80x9ccontactxe2x80x9d ends may be collinear with one another, for effecting connections to electronic components having terminals disposed along a line, such as a centerline of the component.
The present invention addresses and is particularly well-suited to making interconnections to modern microelectronic devices having their terminals (bond pads) disposed at a fine-pitch. As used herein, the term xe2x80x9cfine-pitchxe2x80x9d refers to microelectronic devices that have their terminals disposed at a spacing of less than 5 mils, such as 2.5 mils or 65 xcexcm. As will be evident from the description that follows, this is preferably achieved by taking advantage of the close tolerances that readily can be realized by using lithographic rather than mechanical techniques to fabricate the contact elements.
An object of the present invention is to provide an improved technique for fabricating spring contact elements.
Another object of the invention is to provide a technique for fabricating spring contact elements using processes that are inherently well-suited to the fine-pitch close-tolerance world of microelectronics.
Another object of the invention is to provide a technique for fabricating microminiature spring contact elements directly on active electronic components, such as semiconductor devices, without damaging the semiconductor devices. This includes fabricating microminiature spring contact elements on semiconductor devices resident on a semiconductor wafer, prior to their being singulated therefrom.
Another object of the invention is to provide a technique for fabricating spring contact elements that are suitable for socketing (releasably connecting to) electronic components such as semiconductor devices, such as for performing burn-in on said devices.
According to the invention, a spring contact element is fabricated on an electronic component such as an active semiconductor device by photolithographically defining one or more openings in corresponding one or more masking layers, depositing a conductive metallic mass in the three-dimensional opening(s), then removing the masking layer(s), resulting in a spring contact element which has a base (proximal) end which is adjacent a surface of the component and a contact (distal) end (also xe2x80x9ctip endxe2x80x9d or xe2x80x9cfree endxe2x80x9d) which is both horizontally and vertically spaced apart from the base end. A plurality of spring contact elements can be fabricated in this manner on the component, to photolithographic (extremely fine) tolerances.
The spring contact elements of this invention are suitable for making either temporary or permanent electrical connections to terminals of another electronic component such as a printed is circuit board (PCB).
For making temporary connections, the component upon which the spring contact elements are fabricated is brought together with another electronic component so that the tip ends of the spring contact elements are in pressure contact with terminals of the other electronic component. The spring contact elements react resiliently to maintain contact pressure and electrical connections between the two components.
For making permanent connections, the component upon which the spring contact elements are fabricated is brought together with another electronic component, and the tip ends of the spring contact elements are joined, such as by soldering or brazing or with a conductive adhesive, to terminals of the other electronic component. The spring contact elements are compliant, and accommodate differential thermal expansion between the two electronic components.
The spring contact element is suitably formed of at least one layer of a metallic material selected for its ability to cause the resulting contact structure to function, in use, as a spring (i.e., exhibit elastic deformation) when force is applied to its contact (free) end.
The spring contact elements of the present invention can be fabricated directly on the surface of a semiconductor device, or on the surfaces of a plurality of semiconductor devices resident on a semiconductor wafer. In this manner, a plurality of semiconductor devices resident on a semiconductor wafer can be xe2x80x9creadiedxe2x80x9d for burn-in and/or test prior to being singulated from the semiconductor wafer.
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.